An internal combustion engine typically includes an air induction system with which air is introduced into an intake manifold assembly. In contrast, the air induction system of a turbocharged engine delivers induction air to the impeller of the turbocharger compressor instead of directly to the intake manifold assembly of the engine.
Prior turbocharged induction systems exhibit problems related to the loss of air induction system pressure head. Common attempts to minimize air induction system head loss include the use of short-length air induction systems, large diameter ducting, or ducting with as few directional changes as possible. However, these solutions are not always possible due to the placement of the engine relative to the surrounding vehicle packaging. Additionally, within the design of the system, certain geometry can be used to minimize flow losses, including diffusers and expansion chambers, at a location where flow must pass through a bend or a bell-mouth transition located within the clean air duct upstream of the inlet to the turbocharger.
A diffuser can be utilized to increase the static pressure of fluid passing through the system. Typical conical diffusers provide for a gradual conical expansion of the area encompassed by a system, the rate of area expansion being determined by what is known in the art as the “cone angle.”
Additionally, an expansion chamber or plenum may also be utilized to achieve similar results, under certain conditions. The plenum may encompass an expansion or area increase intended to reduce velocity in order to recover the pressure head of the flow. As air or fluid flow enters the plenum, a reduction in flow velocity occurs. The velocity reduction results in the kinetic energy of the fluid being converted to a static pressure rise due to the conservation of linear momentum and the conservation of angular momentum when swirl is present. Due to the static pressure rise, expansion chambers must be carefully designed to avoid increasing overall head loss.
Furthermore, a bell-mouth transition at the inlet of the turbocharger can be utilized to reduce the amount of head loss and restriction generated as the induction air enters the inlet of the turbocharger.
Although the use of a single approach, such as either a diffuser, an expansion chamber, or a bell-mouth transition, to reduce static pressure losses is well-known, these three features have not been combined in the prior art to obtain the lowest possible turbocharger entrance losses. Moreover, the prior art air induction systems do not utilize a plenum, diffuser, or other means for restoring static pressure head within the area directly in front of the inlet of the turbocharger. Additionally, packaging and manufacturing constraints have often led to design inefficiencies. Prior to the invention, the air induction system would have had to include a plurality of dimensional bends or elbows within the clean air duct to satisfy packaging and design constraints. However, such bends or elbows create a high restriction yielding lower than desired pressure conditions at the inlet of the turbocharger compressor. Furthermore, the prior art air induction systems did not utilize the limited space available after the engine and underhood compartment had already been designed to enhance the flow of induction air.